1. Field of the Invention
The present invention relates to a porous potassium carbonate having a special pore structure and a method for its production.
2. Discussion of Background
Potassium carbonate has a broad range of applications including e.g. production of special glass, soaps or detergents, in the food industry for salt water (ramen noodles additive), and production of pigments. Further, it is often used as a catalyst or a raw material of intermediate ingredients for producing organic chemicals. In such applications, it is desired to provide potassium carbonate having a high velocity of dissolution or a higher activity with respect to its reactivity. For example, JP-A-10-279535 and JP-A-9-188690 disclose to use a potassium carbonate powder having a limited particle diameter and a large specific surface area, but it is still desired to further improve the activity with respect to the reactivity.
Potassium carbonate is mainly produced by two methods, i.e. a direct method to obtain potassium carbonate directly, and a potassium hydrogen carbonate method wherein potassium hydrogen carbonate is firstly obtained and then it is decomposed by calcination to obtain potassium carbonate.
As the direct method, there is a method wherein a carbon dioxide-containing gas is reacted with an aqueous potassium hydroxide solution to obtain potassium carbonate, which is then concentrated to obtain potassium carbonate 1.5 hydrate (K2CO3.1.5H2O), which is then calcined to obtain potassium carbonate. This direct method requires only a small number of instruments for production equipments and has a good productivity, and thus, it has been widely employed. However, in this method, tiny particles (dust) will often be formed at the time of drying after obtaining hydrated potassium carbonate crystals, whereby their handling tends to be difficult. Therefore, it is known to spray the aqueous potassium hydroxide solution directly to the inside of a fluidized bed dryer, and enter a heated carbon dioxide-containing gas thereto, whereby nearly spherical crystals having a high specific gravity can be obtained. However, in potassium carbonate thus obtained by such a method, pores having pore diameters of from 0.1 to 1 μm are hardly observed.
Further, U.S. Pat. No. 5,449,506 discloses a method for obtaining an aqueous potassium carbonate solution directly from potassium chloride by an ion-exchange method. However, the aqueous solution obtained by this method is dilute, whereby it has to go through a concentration process employing large instruments to take out the potassium carbonate, and further, it has been difficult to obtain potassium carbonate crystals having a high activity by the subsequent crystallization.
The potassium hydrogen carbonate method does not have a high productivity like the direct method. However, it is thereby possible to obtain potassium carbonate crystals which are porous and have a large specific surface area, and which have a relatively high activity such as a high reactivity with other chemicals, and a high velocity of dissolution. However, a porous potassium carbonate having a higher activity and a method for its production or manufacturing condition have been unknown.